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Mechanical hazardsScrew (or scroll) extrudersThese machines convey uncured rubber forwards down the barrel and through the die by the action of a rotatingscrew. They produce continuous extruded sections such as cable covering. Single screw versions are most commonbut twin or triple screw extruders may be used for complex products such as cable sheathing where they may beseveral layers of compound (co-extrusion).Screw extruders can be either hot fed, with warmed pre-mixed rubber, or cold fed. Temperature control isgenerally by water circulating in a jacket around the extruder barrel, screw and die head. The rubber is normallyfed in strip form, taken off a two-roll mill.The main mechanical hazard on a single screw rubber extruder is the trap between the rotating screw and thefixed parts of the machine at the feed opening. Feed systems can also create additional trapping hazards such as acrammer feed device.Where rubber is fed in strip form, feed rollers are often used to guide the strip into the feed opening. These maybe free running, or driven in contra- rotating directions so that the strip remains under constant tension. Crammerfeeding with an additional secondary screw is also common.Use adequate fixed or interlocking guards to prevent access to the screw and other dangerous parts, whateverthe feeding arrangement. The simplest arrangement is a series of free running rollers to guide the rubberstrip. These must be spaced to prevent finger access to the screw. Where hinged feed hoppers or feedingdevices are used these should be positively interlocked with movement of the screw.Where powered movement of screen plates (perforated plates which 'strain out' contaminants) create a hazard,additional guarding may be required. The die breaking or being ejected is also a potential hazard. Althoughnot common it occasionally occurs on machines with interchangeable dies where the die or die securing device isworn or inadequate. Regular inspection and maintenance are important.For further information on screw extruders see BS EN 1114. Part 1 covers the extruder, Part 2 die face pelletizers,and Part 3 haul-off devices.Haul-off unitsA lot of reported injuries at extrusion lines occur at haul-offs downstream. These draw off the extruded profilecontinuously to be cured or cooled, and cut to length or reeled up. They operate by pulling the profile by meansof friction between the product and two counter-rotating tracks, belts, or rollers set one above the other. Trappinghazards typically occur between the tracks at the feed position; between the extruded profile and the tracks; andbetween the drive pulleys and tension rollers, and the tracks.When assessing the risk consider: the speed of movement; the forces and pressure applied (including the rigidity of the tracks and the profile); and the method of operation.Use of fixed or interlocking guards should be possible in most cases but guarding of the feed intake may not be soeasy because of the need to allow for different size profiles. The feed opening in the guard should provide adequateprotection for the largest profile handled. Tunnel guards profiled around the sides of the tracks at the feed intake, andmounted on the top and bottom tracks may therefore be a better option. Use of free-running horizontal guide rollers infront of the feed opening will further restrict access.Feeding of product during start-up usually presents the greatest risk to the operator. Where there is a significanttrapping hazard, automatic feeding devices should be used, or feeding should be done with the haul-off stationary.

Where this is not possible a safe system of work is essential. Operate the haul-off at reduced speed, via a hold-to-runcontrol, which should be under the direct control of the operator. BS EN 1114. Part 3 permits a maximum feedingspeed of 200mm/second under these circumstances and gives details of more guarding options.Ram extrudersHere, a roll of rubber compound or 'pig' is placed into the extruder barrel with the die swung out of position; thedie is then closed, either manually or under power, and the rubber is forced through the die by the forward actionof a powered ram. The most common type is the Barwell extruder.Because the extruder is loaded with individual batches of rubber, these machines cannot produce continuousprofiles but produce a strip or pellet for further processing. Where pellets or slugs are produced, the die mayhave a rotating knife (die face cutter).The main mechanical hazard is the trap between the closing die and the barrel on machines where there ispower assisted die closure. Accidents have occurred when a second member of the extrusion team hasattempted to assist die closure by trimming back the rubber during closure.Die closure should be under two hand control and safe systems of work adopted to exclude third parties.Interlock movement of the ram with the die, so that ram movement is not possible with the die swung out ofposition. Rotating knives of die face cutters should have an interlocking guard with appropriate time delay toaccount for run down.

CalenderingIntroductionA calender is a machine with a number of horizontal rolls (sometimes called bowls), heated or unheated, throughwhich material and/or rubber is passed under pressure. They can create either a rubber sheet of a requiredthickness, or apply a thin layer of rubber onto a cloth liner. This is known as frictioning or combining.Cushion calenderCalenders can have two, three or four, rolls of various sizes and configurations. The diagram shows a 4-roll calenderand the material circuits for bilateral coating either textile of metallic fabric or cords.Mechanical hazardsThe main mechanical hazards at calenders are caused by nips between the rolls, for both the rubber andfabric feed. This is a particular problem during threading up, cleaning and maintenance. There is also arunning nip at the take-off or wind-up devices.Depending on the design, there may be other mechanical hazards caused by : auxiliary rollers for embossing or tensioning; cooling drums; cutting devices; stock guides

Rubber feed nipOne of the simplest methods of preventing finger access to the nip is to use a fixed nip bar that extendsthe length of the rolls, positioned no more than 6 mm from the surface of the roll to prevent a trappingpoint.When rubber is fed manually into the nip access can also be prevented using the feed table as a distanceguard, with integrated mesh guards at either end. Dimensions should meet the requirements of BS ENISO 13857:2008 Safety of machinery. Safety distances to prevent hazard zones being reached by upperand lower limbs.There is also a risk of the operator getting entangled with materials and dragged over the table towardsthe nip. To control this risk position a horizontal interlocking trip bar just below and slightly to the front edge ofthe feed table so that the operator cannot approach the nip between the rolls without hitting the trip bar. Thisshould then operate two limit switches, one at each end of the bar and bring the rolls to rest in not more thanan eighth of a revolution.If closer approach is needed for feeding then an interlocked ‘manager guard’ should be used, with dimensionsmeeting the requirements of BS EN ISO 13857:2008. This consists of sturdy parallel bars that prevent fingeraccess to the nip. A push-stick designed to fit between the bars helps feed the rubber to the nips.Fabric feed nipWhen combining, fixed nip guards are often not practical because of the varying thicknesses of material beingcalendered and the need for lower roll adjustment. A ‘limited movement’ guard can therefore be used whichconsists of an interlocking guard of closely spaced bars or hoops/loops. The guard pivots around a horizontal axisand if a hand is drawn between the guard and a roll, the guard operates a position sensor, which stops therolls. After the hand is removed the guard returns to its rest position but this does not cause restarting.Take-off and wind-up devicesRunning nips at various take-off and wind-up rollers, including the coated cloth wind-up mandrel, can create trappingand entanglement hazards. When assessing the risk it is important to take into account: the machine speed;whether the roller or mandrel is powered or not;the sheet tension;the strength and tackiness of the material;the need for approach.Most rubber sheet and rubberised fabric will be very strong when under tension, and capable of inflictingserious injury.Use automatic tensioning equipment, as it should not be necessary for operators to feel or manually adjustthe tension of the cloth whilst it is in motion. Use devices such as slipping clutches to regulate tension, and'banana' or bowed rollers to reduce creasing, as they will also reduce the need for approach.Where there is a significant risk of injury, prevent access to the running nip by interlocking guards, pressuresensitive mats or photoelectric safety systems.For start up, fix the cloth liners to the mandrel whilst it is still stationary.

Adding the fabric liner backing sheet to a cut belt to prevent rubber belt sticking to its self.Note: The backing sheet is re-usedThreading up and maintenanceThreading up and maintenance, including clearing of blockages, can create additional hazards. This is because aclose approach to the nips may be necessary. Where possible threading up and maintenance should be with thecalender stationary and the rolls separated.Where it is necessary to reverse the calender drive, for example to clear blockages, it will create new nips. Reversemovement should be via a hold to run control and at a suitably slow speed, termed an inch device. All operatorsshould also be excluded from the danger areas. If there is more than one operator there should also be flashinglights or an audible alarm. Also, provide sufficient emergency stop buttons on both sides of the calender and at theauxiliary feed and take-off devices.More information on safety during the threading of calenders can be found in SIM 03/2009/07 Safety duringthe XVH of calenders in the rubber DQG SODVWLFV LndustryOther mechanical hazardsThese may include: crushing at the trap between a moving calender roll surface and a fixed part of the machine; crushing between the stock guides and the calender roll; cutting hazard from the blades or trimming knifes; crushing between a swinging feed conveyor and the machine framework; trapping between contra-rotating cooling drums or between drums and fixed parts of the machine; the roll nip adjustment mechanisms.Appropriate procedures should be in place for cleaning and maintenance which are both potentially high risk activities.For further guarding options and requirements, see BS EN 12301 Plastics and rubber machines - Calenders –Safety Requirements

Cloth coatingIntroductionCloth coating involves the impregnation of cloth, mostly synthetic rather than cotton, with a rubber solution toproduce a waterproof or chemically resistant fabric for use in waterproof clothing, tarpaulins, sails, dinghyfabrics etc. A range of rubbers and organic solvents are used to produce the rubber solution or 'dough'.Natural rubber, synthetic polymers such as chlorosulphonated polythene (Hypalon) and urethanes are themost widely used rubbers. Commonly used organic solvents include toluene, xylene, acetone, MEK, andpetroleum naphtha blends (n-hexane based) SBPs 1-5.Rubber compound, produced by internal or open mill mixing, is soaked in solvent before mixing to a solutionwith the consistency of light dough. Colours, other additives and more solvent may be added during mixing.Some fabrics such as nylon require pre-treatment to achieve a good bond with the rubber. MDI is most widelyused as a pre-dip, prior to the spreading process. Most fabrics are pre-dried, usually in a hot air oven, prior tocoating.Spreading machines evenly distribute the rubber solution onto the cloth as it is drawn under it, using anadjustable blade, known as a doctor blade. The coated fabric is then drawn into a drying oven to evaporatethe solvent. The cloth is then passed over cooling rolls and wound up, either at the front or back of themachine. Embossing rollers positioned after the oven produce the desired surface finish. The process isusually repeated a number of times to achieve the required degree of proofing; the coating thickness at eachpass is controlled by adjusting the height of the doctor blade.The rubber solution is fed onto the cloth via a trough or tray. Solutions that are more viscous are added as a'roll' of material directly onto the cloth and adjacent to the doctor blade. The speed of coating machines canvary considerably, from less than 10 metres per minute to over 100 metres per minute. The slower, usuallyolder, spreaders often have steam-heated chests to drive off the solvent. High speed machines tend to useindirect gas-fired evaporating ovens.The coated cloth can be vulcanised by either continuous curing, eg Rotocure, or more commonly by dustingthe coated cloth with a starch based agent to prevent sticking and then re-rolling it and curing it in batches ina steam autoclave.Mechanical and other hazardsThe risk of entanglement and shear trapping hazards at dough mixers should be controlled by havinginterlocking lids, and/or interlocking enclosing guards.As many of the solvents are highly flammable suitably protected electrical devices are required. Also, controlthe risk from static charges. Precautions at evaporating ovens should include explosion relief and flamefailure devicesSpreading machines can have nip and running nip hazards, particularly at the cloth wind-up, embossing, andcooling rollers. Higher production speeds will increase the risk and fixed or interlocking guards or otherprotective devices will be required. At slower speeds and for inaccessible nips, trip wires fitted to emergencystops may be acceptable, if justified in the risk assessment.Safeguarding may also be required for any running nips when the cloth is re-rolled after curing.

Fabrication (including tank lining, roller covering and hose winding)Fabrication covers a range of operations where rubber and other materials are assembled to produce finishedarticles or components. Rubber lining operations and hose building present particular hazards.Rubber lining operationsRubber sheet may be bonded to metal components including valves, pipes, tanks, and rollers, and thenvulcanised to provide a tough, corrosion resistant lining or covering. The main hazards common to all rubberlining operations are the health and fire hazards associated with the use of solvents for degreasing metalcomponents and solvent-based bonding agents. Tank lining and roller covering have additional hazards.Tank liningRubber lining of tanks or other enclosed structures can be either in a factory or on site, but in either caseusually involves the following operations: Clean out the vessel (usually by steam); Prepare the vessel surface (usually by shot blasting); Apply rubber solution, or bonding agent (usually toluene or n-hexanebased); Place sheets of rubber in position (sometimes pre-warmed); Vulcanise (using hot water or steam).These operations present a number of significant hazards, including those associated with entry into confinedspaces; shot blasting; use of flammable and/or toxic solvents; and use of pressure vessels.For any work involving entry into confined spaces, strictly controlled safe operating procedures and highstandards of operator training are essential. Detailed guidance can be found in the Safe work in confinedspaces Approved Code of Practice, Regulations and guidance (L101) and Safe work in confinedspaces Leaflet INDG258.Breathing apparatus will protect the operator against the health hazard associated with solvent use but a fireand explosion hazard may remain. Therefore, use a non-flammable solvent wherever possible. Forcedventilation should reduce the concentration of flammable vapours in air to below one quarter of its lowerexplosive limit. If you can not do this then all potential ignition sources should be excluded and speciallyprotected hand lamps used. Equipment should also be earthed.Small rubber-lined articles are usually cured in an autoclave. Larger tanks or vessels may be converted intotemporary steam receivers by blanking-off the entry point and admitting steam up to 20psi. The requirementsof the Pressure Systems Regulations will then apply. Establish the vessels' safe operating limits and fitprotective devices to protect against and warn of system failure.Roller coveringSteel rollers are covered with rubber or polyurethane sheet as this will provide them with a controlled measureof resilience. They are then cured in autoclaves. In addition to health risks, there is also a danger of fire fromthe solvents and explosion from the fine cured rubber dust produced when grinding the covered roller to size.The majority of reported fires in rubber factories involve finely divided vulcanised rubber and dust. Extractionat rubber grinding machines, depending on the particle size, will generally need to be designed and installedfor use with potentially explosive dusts. Consider where the dust collection unit is located and in particularwhere explosion relief vents to. Good housekeeping will minimise the risks of a secondary dust explosion. Ifthe operator attempts to take too deep a cut, it will cause the rubber to overheat and increase the fire risk.

For more information see Safe handling of combustible dusts: Precautions against explosions(HSG103) and SIM 03/2009/08 Hazardous area classification for explosible dusts in the rubber andplastics industriesHose windingIntroductionRubber hose has a wide variety of applications such as car parts for power steering, air conditioning systems,etc. The most common types are Nitrile and EPDM rubbers but silicones and flouroelastomers are moresuited to high temperature applications.The basic equipment used to produce hose consists of a metal mandrel supported in rotating chucks, one ofwhich is driven. Standard metal working lathes are commonly used.To build up a hose, layers of rubber strip and fabric, with wire or rope used as reinforcing material, are woundonto the mandrel. The wire or rope is applied under tension. The final winding operation involves theapplication under slight tension of nylon webbing known as a spurle. The complete hose assembly

The compound ingredients are fed into an enclosed mixing chamber via a feed hopper and mixed by the shearing action of two winged rotors and the walls of the mixing chamber. There is therefore a contin uous nip. A powered ram or floating weight in the feed throat forces ingredients into the mixing chamber, which is usually water-cooled.